Ideal characteristics of leg wear, such as ladies hosiery, include such properties as: (1) lasting snug fit with quick recovery from stretch out and knee bending, (2) uniform translucent cosmetic appearance with minimum apparent stitch definition, (3) resistance to picks and snags, (4) high durability, and (5) a soft, smooth tactility. Leg wear also ideally possesses "one size fits all" properties, i.e., a wide range of leg sizes can ideally be fit with one hose size, without loss of comfort.
Efforts to impart the above properties to hosiery products have generally involved the use of yams which crimp in the fabrics, by knitting yarns with torque in S and Z directions in alternate courses, or by including a separate elastomer yarn in the hose. Various combinations of these methods have also been used. However, these methods have generally failed to provide hosiery products having the desired physical characteristics and/or have been generally extremely difficult to knit and/or process into satisfactory hosiery products.
Methods for making crimpable yarns have involved, for example, twisting or deforming the yarn or by using differential shrinkage in a two component fiber where the components are eccentrically arranged in the cross-section of the fiber. These techniques are described, for example, in U.S. Pat. Nos. 3,399,108 and 3,779,859. The yarns prepared by twisting, sometimes referred to as "torque yarns", generally have low fit range, poor recovery and exhibit noticeable stitch definition because they must be knit in alternate courses of S and Z directions. Crimpable yarns have also been made by combining together a hard, non-elastomeric polymer with an elastomeric polymer. The yarns prepared by this process, sometimes referred to as "composite" or "conjugate" yarns, are described, for example, in U.S. Pat. No. 4,106,313 and published European Patent Application No. 0 378 194 A2. U.S. Pat. No. 4,405,686 describes a conjugate filamentary yarn which is prepared from composite components including thermoplastic elastomer and non-elastomeric polyarnide or polyester. The yarns disclosed in U.S. Pat. No. 4,405,686 are composed of filaments whose cross-section is a compressed flat shape like a cocoon or oval. This compressed flat shape cross-section is disclosed as being necessary to obtain the highest degree of stretchability.
Hose produced by knitting an elastomeric yarn in combination with a hard yarn, for example, by covering or plaiting, may have good fit and recovery, but are generally difficult to knit.
Prior art yarns which are composed of composite filaments in a side-by-side configuration generally suffer from various drawbacks including, for example a tendency to separate at the interface of the components. In addition, the elastomeric portion of the composite fibers tends to stick to itself when in contact during processing and after packaging. The elastomeric component of the composite fibers also generally exhibits poor abrasion resistance. Prior art efforts to overcome these drawbacks have included spinning the elastomer as a core within a sheath of the hard component. However, the use of sheath-core technology may also be disadvantageous in that it is generally extremely difficult to control sheath thickness and eccentricity, and variations in sheath thickness often lead to non-uniform crimping and dyeing which, in turn, results in reduced yields of the yarns. Sheath core technology also requires highly complex and expensive sheath core spinning equipment and processes.
Prior art composite filamentary yarns must generally be heated and then cooled in a relaxed low-tension zone in order that further heat treatment in hose will develop crimp of an acceptable level. This is undesirable since the additional heat treatment step requires further processing of the fibers, resulting in a more complex process and an attendant increase in manufacturing costs.
Accordingly, new and/or better alternatives to prior art methods and compositions for achieving crimpable fibers and/or yarns are needed. The present invention is directed to this, as well as other important ends.